Remember the $500 million in equity financing at a $15 billion valuation Facebook was going to raise around the time it launched Beacon last fall?

The company never confirmed that it was seeking this much, but, in any event, it didn't get it. Microsoft took $240 million, and Li Ka-Shing and a couple of Germans grabbed about another $150 million (It was reported that these investments were at the same close-to-$15 billion valuation that Microsoft paid; we've heard since that they actually weren't--that Li Ka-Shing and the Germans bought Facebook common stock, not preferred stock, and that they paid a much lower valuation for it--but we haven't been able to confirm/reject this yet).

In any event, now Facebook is taking on $100 million in debt to buy servers. Why is it borrowing the money instead of selling stock? The positive spin, brought to Spencer Ante at BusinessWeek by Facebook and debt lender TriplePoint, is that its a shame for exciting private companies to squander expensive equity on mundane stuff like servers. And that's true up to a point. (Start-up debt financing is a growing trend).

But the real reason you don't often see emerging private companies take on big debt-loads is that borrowing money is riskier than selling stock, and it also subordinates the existing equity holders. The owners of Facebook common stock, for example, now have at least $350 million of claims that have to be paid out of whatever Facebook is ultimately sold for before they get a dime. Given Facebook's current growth, this shouldn't ever be a factor, but you never know.

In any event, Google, Microsoft, Yahoo, eBay, et al, never borrowed money as private companies. And we suspect the real reason Facebook is doing so now is because it couldn't raise the rest of that $500 million round at that $15 billion valuation. Especially now, after the Beacon flop.

According to the numbers Mark Zuckerberg threw out on a conference call last fall, Facebook will burn at least $150 million of cash this year. Given the latest debt deal, we suspect the number is now expected to be considerably higher than that, and Facebook didn't want its cash balances to drop too low. It couldn't sell any more equity at $15 billion, and it didn't want to do a down round, so it turned to the debt markets.

Facebook just borrowed $100 million to build more data centers. The company puts a positive spin on taking on debt, but we suspect it's because Facebook couldn't sell any more stock at that $15 billion valuation.